Isobutylene-based polymers, particularly halogenated isobutylene-based polymers such as brominated butyl rubber are the primary compositions of most tire liners, heat resistant tubes, bladders and other commercial products such as pharmaceutical ware, for example stoppers. Compounds based on butyl polymers are commonly used in a wide variety of applications, and both injection and compression moulding processes may be employed.
U.S. Pat. No. 6,326,433 discloses barrier membranes made from polymeric compositions comprising an isobutylene-based polymer and a semi-crystalline polymer wherein the semi-crystalline polymer has a melting point from about 25° C. to about 105° C. and a heat of fusion from about 9 J/g to about 50 J/g as determined by DSC. The compositions contain at least 15 parts by weight of the semi-crystalline polymer and 10 parts of Flexon, a non-volatile fluid. Column 1, line 28 discloses that isobutylene-based polymers may be used to fabricate molded items such as “pharmaceutical stoppers”.